Electrolytic water treatment

ABSTRACT

An apparatus and method for electrolytically treating water which includes one or more reactors. Each reactor has a liquid containing vessel and one or more pairs of electrodes. The electrodes are suitable for a continuous anodic or cathodic operation for treating water. A power source for each reactor provides voltage and current to the electrodes. A controller maintains the voltage and current provided to the electrodes. The duration of each voltage polarity applied to each electrode is substantially the same. The polarity of the voltage to the electrodes is periodically reversed during which there is a period of zero voltage applied to the electrodes between a first polarity and a second polarity. The period of zero voltage results in a substantial reduction of back e.m.f. of the reactor which enhances the service life and efficacy of the electrodes.

This application is a 371 of PCT/AU95/00203 filed Apr. 11, 1995.

This invention relates to a method and apparatus for water treatment. Inparticular a method and apparatus for water treatment including thecontact of water with electrodes.

BACKGROUND ART

Electrolysis is the process whereby an electric current is used topromote the decomposition of chemical compounds. The use of electrolysisfor treatment of water is known in a number of applications. Theseapplications include the production of ionised water, the production ofhypochlorite from a NaCl solution, the production of hydrogen gas. U.S.Pat. No. 4,384,943 in the name of Stoner describes a method andapparatus for the electrolytic treatment of aqueous fluids to eliminateharmful and other unwanted organisms.

Electrolytic water treatment has also commonly been used for treatmentand chlorination of swimming pool water. An apparatus for thedisinfection of swimming pool water is described in French patent No.2656006 in the name of Levart. This patent describes a device whichproduces chlorine at the rate of 100 g/hr. Processes and means forchlorinating swimming pools are also described in U.S. Pat. No.2,887,444 in the name of Lindsteadt. An electrolytic system for reducingthe bacterial and algal levels in swimming pools which does not involvechlorine production is described in U.S. Pat. No. 4,936,979 in the nameof Brown.

A problem with electrolysis based water treatment equipment is that ascale builds up on one or both electrodes. As the treatment proceedschemical fouling occurs due to oxidation reactions occurring at theanode and reduction reactions occurring at the cathode. Biologicalfouling due to the build-up of neutralised organisms can also occur.

Scale build-up or fouling has a number of detrimental effects on theelectrolysis process. As the scale builds up the current required tomaintain the same potential between the electrodes increases.Conversely, if the current density is to be maintained the potentialbetween the electrodes must be increased. Eventually a limit is reachedwhere further increases in either current or voltage are not possibleand the electrodes must be either cleaned or replaced.

Attempts to minimise the effects of scale formation have followed threeapproaches. One approach has been to develop electrode materials whichminimise the build-up of scale. Another approach has been to putadditives (such as vanadium pentoxide) in the electrolytic solution toslow down deposit formation. The third approach has been to periodicallyreverse the polarity of operation of the electrolysis apparatus andthereby reverse the chemical reactions before appreciable scale build-uphas occurred.

U.S. Pat. No. 1,956,411 by Bonine discloses an automated means forreversal of polarity to increase electrode life. The Stoner inventionreferred to above refers to polarity reversal to increase electrode lifebut asserts that a higher than normal current must be supplied atreversal to complete the change in as short a time as possible, in orderthat as continual as possible a current is applied across theelectrodes. An electrolysis apparatus which includes a manuallyactivated polarity reversing switch is also described in United KingdomPatent No. 2048944 in the name of Spirig.

It is an object of the present invention to provide an apparatus andmethod which includes contacting water with electrodes, to enhance theservice life and efficacy of said electrodes.

An object of one form of the present invention is to provide anelectrolytic water treatment apparatus primarily for chlorination ofswimming pools.

SUMMARY OF THE INVENTION

In one form of the invention although it need not be the only or indeedthe broadest form there is proposed a electrolytic water treatmentapparatus comprising:

one or more reactors, each reactor comprising a liquid containing vesseland one or more pairs of electrodes, and the electrodes being suitablefor continuous anodic or cathodic operation;

a power source for each reactor, said power source providing voltage andcurrent to the electrodes;

a controller adapted to control the voltage and current provided to theelectrodes, and the duration of each voltage polarity applied to eachelectode is substantially the same;

wherein polarity of the voltage to the electrodes is periodicallyreversed and during the reversal there is a period of zero voltageapplied to the electrodes between a first polarity and a second polarityin which period the back e.m.f. of the reactor or reactors issubstantially reduced.

In preference the period of zero voltage is sufficient to allow backe.m.f. between the electrodes to dissipate.

The electrolytic water treatment apparatus may have a multiple number ofelectrodes depending on the reactor output requirements. There may be aneven or odd number of electrodes although an even number is preferable.

In preference the apparatus further comprises one or more fluid pumpswhich cause fluid to flow through the one or more reactors.

In preference the apparatus also includes a number of monitors whichmonitor the operation of the reactor and provide information to thecontroller which may modify the operation of the reactors. Thecontroller can change the voltage, current and polarity in one or moreof the reactors and can change the time that each reactor is on.

Preferably the apparatus includes a voltage restrictor that limits thevoltage of the duty cycle to less than one half the nominal capacity ofthe electrodes.

In an alternative form the invention could be said to reside in a methodof treating a liquid including the steps of passing the liquid to betreated through a reactor, each reactor comprising a liquid containingvessel and one or more pairs of electrodes suitable for continuousanodic or cathodic operation, applying a voltage and a current acrosssaid electrodes such that the duration of the voltage polarity appliedto each electrode is substantially the same, reversing the polarity ofthe voltage to the electrodes periodically, and on reversing thepolarity there is a period of zero voltage applied to the electrodesbetween first polarity and an opposite polarity the duration of such aperiod being sufficient for the back e.m.f of the reactor to besubstantially reduced.

In one form the period of zero voltage is sufficient to allow back e.m.fbetween the electrodes to reduce by at least 50% of the voltage atswitching.

Alternatively the period of zero voltage is such that the sum of thecurrent to which the electrodes are subjected plus the back emf at thetime of switching does not exceed the nominal maximum current densitylimit of said electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding the invention will now be described withreference to several embodiments which will be described with referenceto drawings in which:

FIG. 1 is a block diagram of an electrolytic water treatment apparatusaccording to the invention showing the general control of a reactor,

FIG. 2 is a schematic of a reactor, showing the layout of theelectrodes, a sensor ad housing of the reactor,

FIG. 3 is a part cut-away perspective view of a preferred form ofreactor showing the layout of the electrode plates within the housing,

FIG. 4 is a flow diagram where illustrating the use of multiplereactors,

FIG. 5 is a timing diagram for the operation of one electrode with dutycycles of opposite polarity as well as the dead periods with zerovoltage between the duty cycles,

FIG. 6 exemplifies the range of applications of the invention,

FIG. 7 is a block diagram of control of embodiments having a multiplereactors such as shown in FIG. 4., and

FIG. 8 is a graph of empirical data of an experiment showing decay ofe.m.f. derived from one embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Similar reference characters indicate corresponding parts throughout theseveral views of the drawings.

Dimensions of certain of the parts as shown in the drawings may havebeen modified and/or exaggerated for the purposes of clarity ofillustration.

Referring now to the drawings in detail there is shown in FIG. 1 a blockdiagram of an electrolytic water treatment apparatus. Water entersreactor 1 through pipe 2 under the influence of pump 3 and exits throughpipe 4. Sensors 7 are shown to provide input to a controller 6 fromeither the reactor or perhaps another facility such as a swimming pool.A power source 5 is shown as providing power to the reactors. Thecontroller influences the power source so that a number of parametersmaybe modified. The controller also influences the pump and may alsoinfluence, for example, a brine dosing apparatus in a swimming pool.

The reactor 1 comprises a number electrodes 10 connected, in pairs, bywires 1 and 12, as shown in plan view in FIG. 2, and in perspective inFIG. 3. Power is supplied to the electrodes 10 by a power generator 5.The power generator comprises a transformer connected to a heat sink andrelay. The power generator can be supplied by an external A.C. currentand supplies 9 volts DC to the electrodes. The current can be controlledand varied and it is possible to supply an operating current density ofup to 800 amps per square meter of electrode surface but a differentlimit may be imposed depending upon the nominal maximum limit for theparticular electrodes being used. The control of this power supply willbe described in more detail below.

The reactor vessel comprises a housing 20, made of reinforced glassfibre with a maximum pressure rating of 1300 kPa, and supported withinthe housing are plate electrodes 10, spaced apart from one another,alternatively arranged with one of a first polarity adjacent one of asecond polarity, and supported in that position by nonconductivesupports (not shown). Each electrode comprises an expanded mesh. In theembodiment shown in FIG. 3 each plate is about 300 mm long and 55 mmwide. The electrodes are spaced apart at centres of 6.5 mm. The reactorvessel has an internal cross sectional area of 65 mm by 65 mm and beingperhaps 410 mm long. It is to be understood that these dimensions areonly those of one embodiment and that there could be great variation inthe number of electrodes, in the shape and dimensions and the electrodesand the spacings therebetween. The spacings may also be varied dependingon, amongst other parameters, the conductivity of the medium to bepassed through the reactor, a range of between 2 mm to over 10 mm may beuseful.

The electrodes may be constructed of any material suitable for thepurpose for which they are intended, and variations of electrodessuitable for current reversal are known and may be used. The presentinventors have experimented with titanium electrodes that are suitablycoated, such as with coating known as EC400 or EC600 coatings, and theEC 400 is preferred. Such electrodes are commercially available. Suchelectrodes have a nominal maximum current density capacity of 800 ampsper square meter and therefore as an absolute maximum the power sourceis regulated to provide no more than 800 amps per square meter.

These electrodes have a nominal maximum current capacity of 800 ampsbeyond which their longevity is said to radically decrease. It is foundthat the present reactors are used at a much lower maximum currentdensity of 250-300 amps per square meter for most applications to stillgive a beneficial effect. This is possible because of the manner inwhich they are maintained clean and because use at a lower currentdensity adds to the longevity.

The power supplied to the electrodes 10 is controlled by controller 6.The controller comprises a microprocessor and associated memorycontaining a program that determines the characteristics of the signalapplied to the electrodes 10. The controller may conveniently be acommercially available programmable logic controller (PLC). The outputof power to each of the electrodes is controlled and the polarity of canbe reversed. The controller in most instances may also be used tomonitor a number of other facilities as will become apparent below.

A typical waveform for the operation of each of the electrodes of theapparatus for swimming pool chlorination is shown in FIG. 5. A voltageof one polarity is applied across the lines 11 and 12 for a time τ_(on)determined by the programmed controller. The duration τ_(on) may varyfrom five minutes to 24 hours or perhaps more depending on the specificapplication. After this period τ_(on) the voltage is reduced to zero fora time t_(off) sufficient to allow the back e.m.f. in the cell todissipate to an acceptable level. The voltage is then reapplied but withopposite polarity. The cycle, as depicted in FIG. 5, is repeatedcontinuously.

The τ_(on) period will vary depending upon the deposit or foulingexpected from the application to which the reactor is put. In a typicalswimming pool chlorination application τ_(on) is set at 4 hours andτ_(off) is set at 2 minutes. For other applications with the reactorshown in FIG. 3 the inventors have found that the timings shown in thefollowing table are suitable.

    ______________________________________                                                          τ.sub.on                                                                         τ.sub.off                                        ______________________________________                                        oil/water separation                                                                              15    mins   1 min                                        pool chlorination   4     hrs    2 min                                        drinking water sterilisation                                                                      24    hrs    5 min                                        industrial waste treatment                                                                        1     hr     2 min                                        sewerage            8     hr     2 min                                        ______________________________________                                    

It is found that by periodically reversing the polarity of theelectrodes and allowing time for back e.m.f.'s to settle the fouling ofthe electrodes is substantially reduced, the life of the electrodes isincreased and the efficiency of each cell is maximised.

The operation of the reactor with the above waveform is, it isunderstood, generally not for continuous extended periods, but may beoperated for periods appropriate for the application. Thus for adomestic swimming pool it may only be necessary to activate a reactorfor 2 hours for each day. For a public swimming pool the activation willbe for much greater periods of time and peak periods continuously. Theextent of use that is required can be monitored as will be explainedbelow. For supply of potable water on the other hand it will beunderstood that a continuous treatment is desirable. The time over whichthe reactor is active may be controlled by the controller on a set timebasis, so that where peak use of a swimming pool has been ascertained,the reactor can be active at set times. Preferably however, thecontroller may receive input from sensors reactive to parameterspertinent to the function performed to activate the reactor when limitsfor those parameters are reached.

In many instances it may be desirable to have more than one reactor in abank of reactors 20 such as shown in FIG. 4. Either configured as shownin FIG. 4 to act on a common inlet 21 and outlet 22, or on a separateoutlet or inlet. The controller can be configured to act on each of thereactors separately. When a greater capacity is required, all fourreactors can be active, and when a lesser capacity is required then thereactors can progressively be switched off by turning off the reactorsand appropriate valves 23. This gives a greater flexibility to theextent to which a plant comprising such a treatment apparatus canoperate.

A function of the microprocessor in a multiple reactor apparatus isshown in FIG. 4. In this embodiment mains power to the apparatus issupplied on lines 14. The controller 6 controls the operation ofindividual power controllers 15 (one per reactor). Power from the powercontrollers 15 is transformed by transformers 17. Reversing relays 16are controlled by the controller 6 and determine the polarity of thecurrent supplied to the reactors on lines 19. Signals from a gas monitor(not shown) are supplied to the controller 6 on lines 18. Themicroprocessor selects which cells to activate dependent on treatmentcapacity required. For example, in the embodiment of FIG. 4 two reactorsmay be operated continuously and the other two reactors may only bebrought on line when additional treatment capacity is required. Controllines for valves and sensors have not been shown

In an embodiment useful for a swimming pool the extent of electrolyticactivity required is particularly dependent upon the extent ofdisinfectant in the pool. In such an application the redox value of thesolution in a reactor is monitored by sensor 7 and is provided to thecontroller as an input to the program. Additionally a pH sensor can alsobe provided, or a conductivity meter, readout of both can be provided tothe controller, such that when a limit of each of them or a limitedcalculated from one or more of them is reached the controller activatesor deactivates one or more of the reactors as required.

A further sensor 13 may be provided to measure the potential for thebuild up of gas. The further sensor may be a sensor to measure the flowrate of water through the reactor or pipes leading up to the reactor.The controller switching off the reactor where the flow rate drops belowa limit so that a potentially explosive build-up of gasses does notoccur. It will be understood that where the flow of water stops gasbuild up will occur. The gas monitor provides a safety factor bymonitoring the levels of hydrogen and oxygen in the cells to avoid thebuild up of explosive mixtures.

Where there is a bank of two or more reactors, the controller may alsotake into account manual disconnection of one of the reactors. Thuswhere maintenance of one of the reactors is necessary and removal isnecessary then an appropriate, compensating, level of operation of theother reactors is assumed.

The apparatus may also be operated continuously irrespective of theinputs from the monitors. It will be appreciated that the microprocessorin the controller allows for these and other operating modes to beselectable.

The power controllers 15 also provide a safety factor by having aselectable current limit to prevent current overload of the apparatus.The current limit and the operating current is controlled by thecontroller 6. The current limit for use with the illustrated reactor is25 amps. Given that the total area of electrodes for a reactor is about0.1 meters, the maximum current density for the electrodes will notexceed 250 amps per square meter. This is considerably lower than thenominated maximum capacity of the electrodes of choice (800 amps persquare meter). Given the ability of the present invention to maintainthe cleanliness of the electrodes and the integrity of the electricalconnections that are in contact with the liquid being treated, it isfound that such a level of current is perfectly adequate for mostoperations. The use of a current less than half the nominal maximumcapacity adds to the longevity of the electrodes.

The action of the present invention is not fully understood, however, asuggested explanation is given below. Where current is switched offbetween a pair of electrodes after a duty cycle, a back e.m.f. results,and this is thought to result because of polarisation effects. The back(electromotive force) e.m.f. acts in reverse polarity to that suppliedby the current. Where there is no dead period, and the electrodes arereversed immediately it is suggested that the back e.m.f. adds to thereverse polarity current supplied and the cumulative current has awearing effect on the electrode for the period over which the e.m.f. isoperative. The extra stress on the electrodes or electrical connectionsexposed to the back emf and the liquid being treated can cause extrashedding of the electrode or the exposed electrical component. Thewearing or shedding effect is compounded by the highly reactiveenvironment in which the electrodes operate. Not only is the normalsolution of, for example, the pool having a reactive halogen contentpresent, the environment also has highly reactive gasses and other freeradicals at greatest concentration near the electrodes. Such agents notonly act on compounds present in the water, but also act on theelectrodes, exposed electrical component and on the coatings on theelectrodes. Thus negative aspect of back e.m.f. and current supplyacting on the electrodes are exacerbated by the highly reactive compoundbeing used.

FIG. 8 is illustrative of the results obtained in measuring the backe.m.f obtained by operating in a reactor of the type shown in FIG. 3under conditions present in a swimming pool a concentration of NaCl at2000 ppm. The potential difference across the plates was 9 volts with aduty cycle of 20-25 amperes direct current for a period of 4 hours. Thegraph shows the measurement of back e.m.f. by a voltmeter.

It can be seen that the back e.m.f. occurs essentially instantaneously.The back e.m.f. is initially 15-30% of operating voltage, however thisincreases as duration of duty cycles increases. Visible voltage decay ofback e.m.f. occurs over a period of at least 10 minutes but halveswithin about 2 minutes. The voltage decay is approximately logarithmicbut displays a plateau.

Whilst certain time period of dead time of τ_(off) have been empiricallydetermined as a result of experimentation as set out in Table 1, thesetime periods for τ_(off) however may be varied depending upon thecurrent applied, the solution in which the electrodes are supported andthe nature of the electrodes, as well as a great number of otherfactors. An experiment as conducted above can give a very good guide asto an appropriate dead time for any particular situation.

The decay of back e.m.f. is varied considerably depending upon thecircumstances present. Several influences are detailed below, but it isto be understood however that other influences may also impact. Theplateau is thought to be a function of the dissolved ions in the water.The plateau becomes more pronounced as the length of the duty cycleincreases. It is also found that the rate of voltage decay isproportional with the electrolytic level; thus the rate increases as thepH moves further from neutral. The rate of voltage decay isproportionate with the ease of ionization of the fluid medium. Thusalthough water is neutral it is easily ionizable and therefore aidsincreased rate of voltage decay. The rate of voltage decay is alsoproportional to temperature and inversely proportional the time of theduty cycle. Increased input current will cause a longer decay time. Thisdoes not necessarily means a change in decay rate. Changes of inputvoltage will cause similar variations to decay time.

In a further preferred embodiment the invention has been arranged in amodular fashion on a skid platform. Each module includes: one or morepre-filters, power generators, reactor cells, automatic micron selfcleaning filters, controller and analytic sensing monitors selected frompH, redox, TDS, salinity, temperature, oxygen and specific ions.

The invention may find many applications such as shown in FIG. 4. Itwill be appreciated that variations on the specific embodimentsdescribed will be evident to those skilled in the art but thesevariations will not depart from the spirit of the invention.

Three different applications of the reactor will now be discussed in alittle further detail.

One such application of the invention is in the disinfection of swimmingpools, in particular where Salt water (NaCl) pools are used, to createthe active Cl⁻ component. With large swimming pool applications fourreactors of the type discussed above having 6 electrode plates spacedapart by 6.5 mm are used giving a total area of approximately 0.1 squaremeters. A restrictor is put in place to prevent a current greater than25 amps being supplied to each reactor to give rise to maximum currentdensity of about 250 amps per square meter.

The NaCl under the influence of the highly reactive gasses (H₂ and O₂)produced by the electrodes configure the halogen Cl in a very reactivestate, which is present as a residual disinfectant to maintain the pool.

The swimming pool installation to which this description is directed isa public swimming pool. The plant put into place includes a brine dosingarrangement, release of measured quantities of brine is controlled bythe controller. The plant includes sensors for measuring pH, Redox andConductivity to assess the level of NaCl in the pool water. The level ofNaCl in the water can be measure by conductivity. It is desired to havea level of approximately 3000 p.p.m in water, which equates to aconductivity value of approximately 1800 to 2000 μsiemen. If the valuedrops below 1800 then a measured dose of brine is added to the pool by abrine dosing arrangement.

Similarly a minimum level of disinfectant is specified by the regulatoryauthority, being about 2 mg/liter. A desired level of 2.5 mg/liter ismaintained to ensure that sudden heavy use does not drop thedisinfectant level below 2 mg/Liter. The level of disinfectant can beascertained by the redox sensor or the redox sensor in combination withthe pH sensor, because the disinfectant used is highly oxidising. Aredox level of 650 milli volts is measured as a desirable level. Shouldthe level of disinfectant drop below, for example 2.2 mg/liter when tworeactors are in continuous operation the third and or fourth reactorsmay be activated to provide a boost to the level of disinfectant

In periods of low use, such as perhaps overnight, none of the reactorswill need to be operational continuously to maintain the desired levelof disinfectant.

Two pairs of reactors have been trialled, in the treatment of water inswimming pools, under conditions described above. A first of thereactors had been controlled such that no dead period existed, a secondof the reactors had a dead period as prescribed above. The firstelectrodes failed in approximately 3 and a half months. The electricalconnections leading to the electrodes corroded right through.Additionally the coating on the first electrode had eroded to an extendthat more than half the titanium was exposed. After three months thesecond electrode had no evidence of corrosion either on the electricalconnections or the electrode and is still operating after approximately5 months. It is estimated that the life of the second electrode will beabout 2 years.

Another application of the invention is in the treatment of water toprovide a degree of disinfection and cleaning up of biological and metalresidues. This may be for the pretreatment of water intended to bepotable. Alternatively it may be in the treatment of sewage waste forexample tertiary sewage, before being let out into water ways. Forpotable water, water is to be passed through a reactor at a flow rate ofapproximately 0.25 liters per second to ensure that the retention timein the reactor is sufficient to kill micro-organisms. The action of thehighly reactive gasses and the direct effect of the electric current hasa killing effect that drastically reduces the bacterial and protistcount of the water. Again the longevity of the electrodes is enhancedusing the dead period between reversal of polarity of the electrodes.

Where tertiary sewage is treated (usual discharge from sewage treatmentplants) it is found that the bacterial and protist count is still quitehigh. The turbidity and heavy metal content of the water is also quitehigh. Passing through the reactor of such water drastically reduces themicro-organism count, and the heavy metal content, however it is betterto then pass the so treated water through a membrane filter, to furtherreduce the turbidity and to filter out any heavy metals that may havebeen coagulated with the remaining biological material. The filter is amembrane filter with a nominal separation cut-off of 30,000 daltons.

A third application to be explained is the operation of the invention inthe cleaning up of industrial wastes, in particular where emulsions ofoil are produced. It is found that by introducing a batch of waste intoa settling tank, thereafter passing the emulsion through a reactor, forabout 4 reversals of about 12 minutes each that a settling effect isachieved, with oil being separated to the top of the settling tank,lightly emulsified solution comprises the bulk of the material, andsettles to the middle of the tank, and a sediment sludge forms to thebottom of the tank. After treatment with the reactor the lightlyemulsified solution can be passed through a filter to filter out theoil, appropriately, with a very much increased life of the filter beingachieved. The water being sufficiently good to discharge into waterways.

A further application of the invention is to provide an apparatus whichis capable of removing from water one or more of: colloidal solids;metals; chemicals; oils; complex carbohydrates; carbonates; phosphates;nitrogen; ammonia; and pesticides.

A still further application of the invention to provide an apparatususeful for one or more of: drinking water processing; effluenttreatment; sewerage treatment; process water treatment; conditioning ofcooling circuit water; control of legionella, waste water treatment fordischarge; waste water treatment for re-use; and prevention ofprecipitates in water storage systems.

We claim:
 1. An electrolytic liquid treatment apparatus comprising:atleast one reactor for containing a liquid, the reactor or each reactorcontaining at least a pair of electrodes for immersion in and treatmentof the liquid; power supply means with a pair of wires connected to theelectrodes to provide voltage across the electrodes and current to theelectrodes, the power supply means including controlled switch means forinterruption of voltage across the electrodes and for changing which ofthe pair of wires are connected to which the electrodes therebyproviding means to change a polarity of voltage across said electrodes;and controller means to control wear of the electrodes by control ofcurrent generated by back E.M.F. between electrodes, the control meanscontrolling the controlled switch means so that voltage across theelectrodes is of a first polarity, then interruption of voltage for aperiod of time to enable substantial reduction in back E.M.F. betweenelectrodes, and application of voltage to the electrodes of a secondpolarity opposite to the first polarity.
 2. An apparatus as in claim 1comprising electrodes suitable for continuous anodic and cathodicoperation.
 3. An apparatus as in claim 1, wherein the period of time ofvoltage interruption is sufficient to allow the back E.M.F. to reduce byat least 50%.
 4. An apparatus as in claim 1 wherein the period of timeof voltage interruption is sufficient to allow the back E.M.F. to reduceby at least 80%.
 5. An apparatus as in claim 1 wherein the period oftime of voltage interruption is sufficient to allow current surge atapplication of voltage of the second polarity to be less than a maximumrated current for the electrodes.
 6. An apparatus as in claim 1 whereinthe period of time of voltage interruption is sufficient to allowcurrent surge at application of voltage of the second polarity to beless than 60% of a maximum rated current for the electrodes.
 7. Anapparatus as in claim 1 wherein the electrodes are made of titaniumcoated with a coating EC400, and the period of time of voltageinterruption is sufficient to allow electrode current density forelectrode surface area during current surge at application of voltage ofthe second polarity to be less than 800 amps per square meter.
 8. Anapparatus as in claim 1 wherein the electrodes are made of titaniumcoated with a coating EC800, and the period of time of voltageinterruption is sufficient to allow electrode current density forelectrode surface area during current surge at application of voltage ofthe second polarity to be less than 800 amps per square meter.
 9. Anapparatus as in claim 1 wherein the period of time of voltageinterruption is greater that 1 minute.
 10. An apparatus as in claim 1wherein a period of time of voltage of the second polarity issubstantially the same as a further period of time of voltage of thefirst polarity and each period of voltage of the first or secondpolarity is greater than 1 minute.
 11. An apparatus as in claim 1wherein a period of time of voltage of the second polarity issubstantially the same as a further period of time of voltage of thefirst polarity and each period of voltage of the first or the secondpolarity is greater that 15 minutes.
 12. An apparatus as in claim 1wherein a period of time of voltage of the second polarity issubstantially the same as a further period of time of voltage of thefirst polarity and each period of voltage of the first or the secondpolarity is greater than 23 hours.
 13. An apparatus as in claim 1wherein a period of time of voltage of the second polarity issubstantially the same as a further period of time of voltage of thefirst polarity and each period of voltage of the first or the secondpolarity is greater than 3 hours.
 14. An apparatus as in claim 1 whereinthe reactor or each reactor contains an even number of electrodes. 15.An apparatus as in claim 1 wherein the controller means furthercomprises at least one monitor which monitors the operation of thereactor or each reactors, and the controller means controls thecontrolled switch means in response to the monitored operation of thereactor or each reactor by adjusting one or more of magnitude of voltageacross the electrodes, current flowing through the electrodes, polarityof voltage across the electrodes, period of time of the first or secondpolarity, and period of time of voltage interruption between voltage offirst and second polarity.
 16. An apparatus as in claim 1 furthercomprising fluid inlet means connected to the reactor or each reactorfor carrying liquid thereto, fluid outlet means connected to the reactoror each reactor for carrying liquid therefrom, and one or more liquidpumps connected to the fluid inlet means for pumping liquid through thereactor or each reactor.
 17. An apparatus as in claim 16 wherein thecontroller means further comprises a flow meter means to measure theflow of liquid through the reactor or each reactors, and interruptsvoltage across the electrodes when the flow of liquid is below apredetermined flow rate.
 18. An apparatus as in claim 1 furthercomprising redox probe means for measuring the redox of the liquid,solids dosing means for dosing the liquids with solids, and thecontroller means activates the solids dosing means to dose the liquidwhen the redox of the liquid as measured by the redox probe is pastpredetermined level.
 19. An apparatus as in claim 1 wherein the powersupply means further includes current restricting means to restrictcurrent flow from the power supply means through the electrodes.
 20. Anapparatus as in claim 19 wherein the current restricting means limitscurrent from the power supply means form the electrodes to less than 50%of a maximum current rating of the electrodes.
 21. A method of treatinga liquid with an electrolytic liquid treatment apparatus comprising:(a)providing at least one reactor for containing a liquid, the reactor oreach reactor containing at least a pair of electrodes for immersion inand treatment of the liquid; (b) providing a power supply means with apair of wires connected to the electrodes to provide voltage across theelectrodes and current to the electrodes, the power supply meansincluding controlled switch means for interruption of voltage across theelectrodes and for changing which of the pair of wires are connected towhich of the electrodes thereby providing means to change a polarity ofvoltage across said electrodes; (c) controlling the controlled switchmeans so as to apply voltage across the electrodes of a first polarity;(d) interrupting voltage between the electrodes for a period of time toenable substantial reduction in back E.M.F. between electrodes; and (e)applying voltage to the electrodes of a second polarity opposite to thefirst polarity, whereby the method controls wear of the electrodes bycontrol of current generated by back E.M.F. between electrodes.
 22. Amethod as in claim 21 wherein the step of interrupting voltage is for aperiod of time is sufficient to allow the back E.M.F. to reduce by atleast 50%.
 23. A method as in claim 21 wherein the step of interruptingvoltage is for a period of time is sufficient to allow the back E.M.F.to reduce by at least 80%.
 24. A method as in claim 21 wherein the stepof interrupting the voltage is a period of time is sufficient to allowcurrent surge at application of voltage of the second polarity to beless than a maximum rated current for the electrodes.
 25. A method as inclaim 21 wherein the step of interrupting the voltage is for a period oftime is sufficient to allow current surge at application of voltage ofthe second polarity to be less than 60% of a maximum rated current forthe electrodes.
 26. A method as in claim 21 for controlling anelectrolytic liquid treatment apparatus with electrodes made of titaniumcoated with a coating EC400, wherein the step of interrupting thevoltage is for a period of time is sufficient to allow electrode currentdensity for electrode surface area during current surge at applicationof voltage of the second polarity to be less than 800 amps per squaremeter.
 27. A method as in claim 21 for controlling an electrolyticliquid treatment apparatus with electrodes made of titanium coated witha coating EC800, wherein the step of interrupting the voltage is for aperiod of time is sufficient to allow electrode current density forelectrode surface area during current surge at application of voltage ofthe second polarity to be less than 800 amps per square meter.
 28. Amethod as in claim 21 the step of interrupting the voltage is for aperiod of time greater than 1 minute.
 29. A method as in claim 21wherein the step of applying voltage of the second polarity is for aperiod of time which is substantially the same as a further period oftime of the step of applying voltage of the first polarity and eachperiod of voltage of the first or second polarity is greater than 1minute.
 30. A method as in claim 21 wherein the step of applying voltageof the second polarity is for a period of time which is substantiallythe same as a further period of time of the step of applying voltage ofthe first polarity and each period of voltage of the first or the secondpolarity is greater than 15 minutes.
 31. A method as in claim 21 whereinthe step of applying voltage of the second polarity is for a period oftime which is substantially the same as a further period of time of thestep of applying voltage of the first polarity and each period ofvoltage of the first or the second polarity is greater than 1 hour. 32.A method as in claim 21 wherein the step of applying voltage of thesecond polarity is for a period of time which is substantially the sameas a further period of time of the step of applying voltage of the firstpolarity and each period of voltage of the first or the second polarityis greater than 3 hours.
 33. A method as in claim 21 for a controllermeans further comprising at least one monitor for monitoring theoperation of the reactor or each reactor, and the method including thestep of controlling the controlled switch means in response to themonitored operation of the reactor or each reactor by adjusting one ormore of magnitude of voltage across the electrodes, current flowingthrough electrodes, polarity of voltage across the electrodes, period ofthe first or second polarity, and period of the voltage interruptionbetween voltage of the first and second polarity.
 34. A method as inclaim 21 for an electrolytic liquid treatment apparatus that furthercomprising fluid inlet means connected to the reactor or each reactorfor carrying liquid thereto, fluid outlet means connected to the reactoror each reactor for carrying liquid therefrom, one or more liquid pumpsconnected to the fluid inlet measure for pumping liquid through thereactor or each reactor, and a flow meter means to measure the flow ofliquid through the reactor or each reactor, wherein the method includesthe step of interrupting voltage across the electrodes when the flow ofliquid is below a predetermined flow rate.
 35. A method as in claim 21for an electrolytic liquid treatment apparatus further comprising redoxprobe means for measuring the redox of the liquid, solids dosing meansfor dosing the liquid with solids, wherein the method includes the stepof activating the solids design means to does the liquid when the redoxof the liquid as measured by the redox probe is past a predeterminedlevel.